1. Field of the Invention
Reticuloendotheliosis viruses (REVs) are a group of serologically related retroviruses antigenically distinct from avian leukosis retroviruses (ALVs). REV isolates have been obtained from turkeys, pheasants, chickens, and ducks. These isolates have been classified into three subtypes based on cross neutralization with polyclonal antisera and indirect immunofluorescence with monoclonal antibodies. Representative REVs include strain T (subtype 1), chick syncytial (CS; subtype 3), spleen necrosis (SN; subtype 2), and duck infectious anemia (DIA; subtype 2) viruses. Using a combination of monoclonal antibodies (MAbs) in indirect fluorescent-antibody test and in cross-neutralization tests with chicken sera, Chen et al. [Arch. Virol. 93: 233-245 (1987)] have defined three antigenic subtypes among 26 REV isolates studied.
REV causes immunodepression, neoplams, and runting in chickens. It has also been implicated in contaminated Marek's disease vaccines. The occurrence of REV in turkeys and the presence of REV antibodies in Japanese quails with lymphoproliferative disease suggest that REV infection may be widespread. Moreover, morphologic similarities to peripheral nerve lesions associated with Marek's disease necessitates specific diagnostic assays to provide unequivocal evidence of REV infection.
Although Cho [Avian Dis. 27: 261-270 (1983)] reported focus formation of REV in quail fibroblasts, infection of REV is not consistently cytopathic in chicken cells.
2. Description of the Prior Art
Witter et al. [J. Natl. Cancer Inst. 45: 567-577 (1970)] have reported on an immunofluorescence assay for REV, and a specific REV micro-complement-fixation test has been reported by Smith et al. [Avian Dis. 21: 612-622 (1977)]. However, both tests require adequate REV replication and amplification and are therefore cumbersome for mass screening of flocks. Ianconescu [Avian Pathol. 6: 259-267 (1977)] and Bagust [Avian Pathol. 8: 375-389 (1979)] used agar gel precipitation (AGP) to detect REV in experimentally infected chicken plasmas and sera, but the limits of sensitivity were not reported. AGP is relatively insensitive and also requires REV propagation.
Cui et al. [Avian Dis. 32: 32-40 (1988)] have described an enzyme-linked immunosorbent assay (ELISA) which uses a mixture of MCAs prepared against a 62-kilodalton (kd) REV envelope glycoprotein (gp 62) to detect REV antigen. The MAbs 11A25 and 11C237 each recognize a different epitope, so that the combination of the two in ELISA result in enhanced sensitivity of detection. However, unlike MAb 11A25, which is cross-reactive with all three subtypes, MAb 11C237 reacts only with subtypes 1 and 3.
A successful monoclonal-mediated ELISA must meet several criteria including the ability of the MAb to recognize a major common epitope of the virus, the ability of the MAb to recognize different epitopes on the same protein molecule, and the ability of these MAbs when combined to give a synergistic additive effect to enhance sensitivity.